The goal of the proposed research is to elucidate the molecular mechanisms whereby an excitable cell exerts a trophic influence on another excitable cell. The work will be carried out in tissue culture using clonal nerve and muscle cell lines. Purified neurotoxins, anti-acetylcholine receptor antisera, and monoclonal anti-acetylcholine receptor antibodies will be used to investigate the mechanisms whereby a nerve cell regulates synthesis, degradation and distribution of acetylcholine receptors on nerve and muscle. Additional probes of ganglionic nicotinic receptors, such as substance P, will be used to provide access to these molecules. A renewed effort will be made to isolate mutant cell lines of nerve and muscle for investigations into the biochemistry and interaction of these cells.